Patent GB-627326-A (GB)
Title: Improvements in or relating to burner control
IPC: F23N5/08
Filed: 1946-10-11
Abstract: 627,326. Liquid-fuel burners. COMBUSTION CONTROL CORPORATION. Oct. 11, 1946, No. 30428. Convention date, Oct. 12, 1945. [Class 75(i)] [Also in Groups XL(b) and XL(c)] Electronic relay apparatus for the control of a fluid fuel burner comprises a triode electron discharge device where in the control electrode is connected to an AC supply point through means for passing current in one direction only and to another AC supply point through a capacitance, and the circuit includes in series the capacitance, the said means, the AC supply points, and means effective when the said means is bridged by a resistor which will pass current in either direction, to charge the capacitance in a direction tending to render the control electrode negative with respect to the cathode. The burner may be included in a house heating installation and be provided with flame responsive means connected with the control electrode of the triode, whereby in the event of failure of the flame the triode is rendered non-conductive to de-energise a relay controlled by the latter, which in turn de-energises a further relay to cut off the power supply to the burner motor. The burner 1, Fig. 1, is controlled by a room thermostat 3 having contacts f and j. When the temperature falls below a certain value first contact j closes, then the contact f. Only after the latter has closed a relay M3 becomes energised to close contact v, to complete the circuit through the burner ignition device 12, and to close a contact w to energise a relay M2. The closing of the contact f also energises the filaments of a double triode T in a circuit including a multiple switch controlled by bimetallic elements 5, 6 heated by coils h 1 , h 2 . The relay M2 closes a contact b to establish a holding circuit through a switch s whereby the relay M2 is not de-energised unless both contacts f and j are broken, and also closes a contact e completing the circuit of the burner motor. The switch s is maintained closed by a relay M1 controlled by the double triode T, the grid g 1  of which is connected to a photo tube P energised by light from the burner flame. The bias on the grid g 1 , is thereby reduced and the tube T rendered conductive. In the event of the flame being extinguished the tube T is rendered non- conductive by the charging of the condenser C1. by grid current, and the relay M1 is de-energised. The switch s is opened to de-energise the relay M2 and the switch e opens to cut off the burner motor 12. Should deterioration of the photo-tube P set up a leakage path equivalent to a parallel resistance R6 the double triode would tend to remain conductive in the event of flame failure, and in order to prevent this a resistor R4 is provided in the grid circuit of the second half of the double triode T, whereby grid current through the resistor R4 sets up a potential tending to maintain the grid g 1  negative with respect to the cathode k 1 . An alternative control system is described in which the burner igniter is continuously energised and no relay is provided in its supply circuit. The photo tube P may be replaced by any other flame detecting rectifying device, e.g. a rod arranged to make contact with the earth through the flame. U.S.A. Specification 2,425,164 is referred to.